In recent years, a wireless sensor network has attracted attention, in which sensors are mounted on wireless communication devices and a management apparatus, such as a gateway (GW), collects pieces of measurement data from the sensors by multi-hop ad hoc communication. The wireless communication devices in the wireless sensor network need not perform network configuration, such as configuration of an Internet protocol (IP) address or a GW, and after being deployed in the network, autonomously determine a route to a final destination device.
For example, each of the wireless communication devices exchanges a control message with a neighboring device that is enabled to communicate with the subject device via a single hop, to thereby mutually recognize their existence. Furthermore, each of the wireless communication devices includes routing information stored therein into the control message to be transmitted, to thereby exchange the routing information with the neighboring device. In this manner, by exchanging the control message in the wireless sensor network, each of the wireless communication devices determines a route to a final destination device.
As a frame transmission system used in the wireless sensor network, a carrier sense multiple access (CSMA)/collision avoidance (CA) system employed in the wireless local area network (LAN) standard IEEE 802.11b is known. In the CSMA/CA system, received power strength (received signal strength indication (RSSI)) is monitored to avoid radio collision. If the RSSI is below a certain value, it is determined that other devices are not performing transmission, and after a wait for a certain time, a frame is transmitted. The wireless communication device that has transmitted the frame repeats retransmission the designated number of times until receiving an ACK from the transmission destination. Furthermore, if the wireless communication device does not receive the ACK after repeating the retransmission the designated number of times, the wireless communication device changes the transmission route to another route and transmits the frame through the changed route.
Patent document 1: Japanese Laid-open Patent Publication No. 2009-267532
Patent document 2: Japanese Laid-open Patent Publication No. 2010-233187
Patent document 3: International Publication Pamphlet No. WO 2011/013165
Incidentally, in the conventional technology, it is possible to improve the frame reachability by increasing the number of retransmissions. In contrast, the occupancy of the radio band increases by the increase in the number of retransmissions. Namely, improving the frame reachability by the increased number of retransmissions and ensuring the radio band are in a trade-off relationship, and can hardly be realized at the same time.
For example, in the conventional technology, even when a primary route is switched to a redundant route due to a failure in transmission of a frame, it may be possible that the redundant route is an unstable route with weaker signal strength than that of the primary route and retransmission may be repeated the maximum number of times. In contrast, in some cases, the signal strength does not differ between the primary route and the redundant route. In this case, it may be possible to improve the frame reachability by switching the route.
Incidentally, the OSI reference model is known as a model that divides a communication function of a communication apparatus into layers. In the OSI reference model, an ideal communication system is such a system that causes each of the layers to perform a process, such as parameter operation or function-call operation, without influencing the other layers, that is, that reduces the dependency.
In the conventional technology, routing control for selecting and switching a route to a destination is performed by the third layer, and retransmission control for transmitting and retransmitting a frame is performed by the second layer. Therefore, the retransmission control and the routing control are independent of each other and is not performed in an associated manner. Therefore, the frame reachability is improved by increasing the number of retransmissions, but in contrast, the radio band is occupied due to the increased number of retransmission processes.